Good questions. I just want to share some information:
- Daedessa, the Builder, and Corvus properties are mentioned in the Book of Tyrael. So it seems the ideas are part of Diablo lore for the last years.
- Malthael attacked Tyrael as soon as possible because he feared Corvus city properties.
- Malthael wiped 90% of mankind in ALL Sanctuary. However, he took special attention to Westmarch. Tyrael was there, and maybe Blizzard can say that strategically the Immortal and Shadows needed to be eliminated first. Maybe...Malthael destroyed those factions forever.
However, the Book of Tyrael didny mention Immortals or Shadows hehe, how this factions hid from the angel of Justice??? haha